A model for the net entrapment of fine suspended sediment in the viscous sublayer of a turbulent boundary layer yields an expression of the same form as one derived previously on an empirical basis. The expression is modified by a factor that takes into account the reduction in rate of deposition caused by occasional erosion, bottom roughness, and organic resuspension. A curve for the variation in critical deposition shear stress with particle settling velocity is constructed using the assumption that the critical deposition stress is equal to the critical erosion stress for fine noncohesive material. Application of the model to postglacial deposition rates using modern concentration data gives reasonable agreement and suggests values of the factor little less than unity. The model involves assumption of a constant near-bed suspended sediment concentration. An alternative case of decrease in concentration with distance along the flow path shows that the grain-size modes in the deposited sediment resemble the pattern of size modes found north of the Carnegie Ridge in the Panama Basin.